Gamma Knife radiosurgery has long been the treatment of choice for many brain tumors and functional disorders. According to Leksell Society treatment statistics, in 2006 alone a total of 57,768 patients received Gamma Knife radiosurgery for brain tumors and functional disorders.
In a Gamma Knife radiosurgery, γ-rays emitted from radioactive sources are used to eradicate tumors. These sources are placed in a hemispherical, linear, or circular array and their γ-ray beams are focused to a single point, creating a spherical high dose volume. Current Gamma Knife systems can produce spherical high dose volumes of different sizes by either external beam collimators (e.g., the patient's helmet system in the Gamma Knife® C™ System) or automatic built-in beam collimators (e.g., in the Gamma Knife® Perfexion™ system).
In practice, Gamma Knife radiosurgery consists of a planning phase and a delivery phase. In the planning phase, a ball-packing approach is used for planning Gamma Knife treatment, whose goal is to “pack” the different sized spherical high-dose volumes (called “shots”) into the target tumor volume to create a conformal radiation dose distribution. Thus, a Gamma Knife radiosurgery plan is basically a set of planned shots whose locations, sizes and beam-on times are determined.
In the delivery phase, a Gamma Knife treatment plan is delivered in a “step-and-shoot” manner. A Gamma Knife head frame will be surgically attached to the patient's skull to establish a reference coordinate system. For each planned shot, the patient is first positioned with respect to the attached head frame before being moved into the source housing unit to receive the shot. Since repositioning is an off-line procedure (i.e., performed when the patient is outside the source housing unit and not being exposed to radiation), a Gamma Knife treatment can be very time consuming.
Besides prolonged treatment times, current ball-packing based Gamma Knife treatment also has more serious drawbacks. Packing is a venerable topic in mathematics. Most packing problems exhibit substantial difficulty. Even restricted 2D versions have been proved to be computational intractable and have significant high time complexity. So far, there is no computer-based automatic commercial planning system for Gamma Knife radiosurgery.
Instead, Gamma Knife treatments are mostly planned by humans through trial-and-error. Since the planner has to adjust many parameters (such as the number of shots, the locations, beam-on times and sizes of the shots) in a complex 3D anatomy, it is difficult and time-consuming to develop a high quality treatment plan. As a result, current Gamma Knife treatment can only prescribe a single isodose line (40-50% of the maximum dose) to cover the peripheral of the target tumor volume and leaves high dose spot randomly scattered inside the target. This inability to prescribe multiple isodose distributions limit the applications of functional imaging techniques such as magnetic resonance spectroscopy (MRS), which can reveal high tumor burden regions that require dose escalations to sub-regions inside the targeted tumor with multiple isodose distributions.
Accordingly, it would be advantageous to develop a dynamic scheme for Gamma Knife radiosurgery based on the concept of “dose-painting” to take advantage of robotic patient positioning system on the Gamma Knife C and Perfexion units.
It would be advantageous to develop a dynamic scheme for Gamma Knife radiosurgery in which the spherical high dose volume created by the Gamma Knife unit will be viewed as a 3D spherical “paintbrush”.
It would also be advantageous to develop a dynamic scheme for Gamma Knife radiosurgery in which the treatment planning reduces to finding the best route of this “paintbrush” to “paint” a 3D tumor volume.
It would also be advantageous to develop a dynamic scheme for Gamma Knife radiosurgery in which the patient is moving continuously under the robotic positioning system.